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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Structure of Molybdenum and Tungsten Sulfide M_xS_y~+ Clusters: Experiment and DFT Calculations
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Structure of Molybdenum and Tungsten Sulfide M_xS_y~+ Clusters: Experiment and DFT Calculations

机译：钼和钨硫化物M_xS_y〜+团簇的结构：实验和DFT计算

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A combination of experiment and density functional theory was used to investigate the energetics of CO adsorption onto several small M_xS_y~+ (M = Mo, W; x/y = 2/6, 3/7, 5/7,6/8) clusters as a probe of their atomic and electronic structure. Experimentally, tandem mass spectrometry was used to measure the relative yields of M_xS_y~+(CO)_n cluster adducts formed by collisions between a beam of mass-selected M_xS_y~+ cluster ions and CO molecules in a high-pressure collision cell (hexapole ion guide). The most probable M_xS_y~+(CO)_n adducts observed are those with n≤ x, that is, only one CO molecule bound to each metal site. The notable exception is the M5S_7~+ cluster, for which the n =6 adduct is found to have nearly the same intensity as the n = x = 5 adduct. Density fuctional calculations were used to search for the lowest energy structures of the bare M_xS_y~+ clusters and to obtain their relative stability for sequential CO binding. The calculated trends in CO binding energies were then compared to the experimental adduct distributions for assigning the ground-state structures. In this way, it was possible to distinguish between two nearly isoenergetic ground-state isomers for the M2S_6~+ and M3S_7~+ clusters, as only one isomer gave a calculated CO stabilization energy trend that was consistent with the experimental data. Similar comparisons of predicted and observed CO adsorption trends also provide evidence for assigning the ground-state structures of the M5S_7~+ and M6S_8~+ clusters. The latter contain metallic cores with most of the sulfur atoms bonded along the edges or in the faces of the metal core structure. The n = 6 and 7 adducts of M5S_7~+ are predicted to be more stable than the n =x= 5 adduct, but only the n = 6 adduct is observed experimentally. The DFT calculations show that the n = 1 adduct undergoes internal bond breaking whereas the n= 6 framework is stable, albeit highly distorted. For the M6S_8~+ cluster, the calculations predict that the two lowest energy isomers can bind more than six CO molecules without fragmentation; however, the apparent binding energy drops significantly for adducts with n > 6. In general, the ability of these small M_xS_y~+ clusters to bind more CO molecules than the number of metal atoms is a balance between the gain in CO adsorption energy versus the strain introduced into the cluster structure caused by CO crowding, the consequences of which can be fragmentation of the M_xS_y~+(CO)_n cluster adduct (n > x).
机译：实验和密度泛函理论的结合被用来研究CO吸附到几个小的M_xS_y〜+（M = Mo，W; x / y = 2/6，3/7，5 / 7,6 / 8）上的能量学团簇作为其原子和电子结构的探针。在实验上，串联质谱用于测量在高压碰撞池（六极离子）中质量选择的M_xS_y〜+簇离子束与CO分子之间的碰撞形成的M_xS_y〜+（CO）_n簇加合物的相对产率指南）。观察到的最可能的M_xS_y〜+（CO）_n加合物是n≤x的加合物，也就是说，每个金属位点仅结合一个CO分子。值得注意的例外是M5S_7〜+团簇，其n = 6加合物的强度与n = x = 5加合物的强度几乎相同。密度泛函计算用于寻找裸M_xS_y〜+团簇的最低能级结构，并获得其相对稳定性，以进行连续的CO结合。然后将计算得出的CO结合能趋势与用于确定基态结构的实验加合物分布进行比较。这样，就有可能区分出M2S_6〜+和M3S_7〜+团簇的两个近等能量基态异构体，因为只有一个异构体给出了计算出的CO稳定能趋势，与实验数据一致。预测和观察到的CO吸附趋势的相似比较也为确定M5S_7〜+和M6S_8〜+团簇的基态结构提供了证据。后者包含金属核，其中大部分硫原子沿着金属核结构的边缘或表面键合。预测M5S_7〜+的n = 6和7加合物比n = x = 5加合物更稳定，但实验上仅观察到n = 6加合物。 DFT计算表明，n = 1加合物发生了内部键断裂，而n = 6骨架是稳定的，尽管高度扭曲。计算结果表明，对于M6S_8〜+团簇，两个最低能量异构体可以结合六个以上的CO分子而不会发生断裂。但是，对于n> 6的加合物，表观结合能显着下降。通常，这些小的M_xS_y〜+团簇结合更多的CO分子而不是金属原子数量的能力是CO吸附能与由CO拥挤引起的引入到簇结构中的应变，其后果可能是M_xS_y〜+（CO）_n簇加合物的碎片化（n> x）。

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